Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2008 through 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results from the EPA/IDNR fish tissue monitoring program in 2001, 2005, 2007, and 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to levels of indicator bacteria that exceed state water quality standards. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (monitored) as “partially supported” due to the existence of a fish consumption advisory. The Class C (drinking water) uses are “not assessed” due to a lack of information upon which to base an assessment. Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program from 2008 through 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results from the EPA/IDNR fish tissue monitoring program in 2001, 2005, 2007, and 2009.
Note: A TMDL for turbidity at Nine Eagles Lake was prepared by IDNR and approved by EPA in 2001. Through implementation of this TMDL, water clarity at this lake had improved such that the lake was de-listed for the 2004 assessment/listing cycle. Because, however, the 2006, 2008, 2010, and 2012 Section 303(d) impairments due to indicator bacteria and mercury in fish tissue at Nine Eagles Lake were not addressed in the TMDL, this waterbody remains in Category 5a (impaired; TMDL required) for the 2012 cycle.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Nine Eagles Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (24 samples), 2009 (27 samples), and 2010 (17 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Nine Eagles Lake beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 66 E. coli orgs/100 ml in 2008, 53 E. coli orgs/100 ml in 2009, and 77 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 21% in 2008, 19% in 2009 and 29% in 2010. The percentage of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2008 and 2010 and therefore suggests impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses at Nine Eagles Lake are “fully supported.” Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 50, 49, and 53 respectively for Nine Eagles Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Nine Eagles Lake in the eutrophic category, while the chlorophyll a value places Nine Eagles Lake in the mesotrophic category. These values suggest extremely low levels of chlorophyll a and suspended algae in the water, very good water transparency, and low levels of phosphorus in the water column.
The level of inorganic suspended solids is low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Nine Eagles Lake was 1.6 mg/L, which was the 3rd lowest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a small population of cyanobacteria exists at Nine Eagles Lake, which does not suggest impairment at this lake. These data show that cyanobacteria comprised only 55% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (5.9 mg/L) was also the 12th lowest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. The ISU and UHL lake surveys show that during 2006-2010 there were no violations of the Class B(LW) criterion for ammonia in 22 samples, for dissolved oxygen in 22 samples, or for pH in 22 samples. Based on IDNR’s assessment methodology these results suggest full support of the Class B(LW) uses at Nine Eagles Lake.
The Class C (drinking water) uses are "not assessed" due to lack of monitoring data upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2006-10 show that nitrate levels are generally low at this lake (maximum value = 8.4 mg/l; median = 0.1 mg/l) compared to the drinking water MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “partially supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Nine Eagles Lake in 2001, 2005, 2007, and 2009. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The level of mercury in the samples of largemouth bass in 2001 (0.26 ppm) exceeded the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory (this level is well below the “do not eat” trigger level for mercury of 1.0 ppm). According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. Because the level of mercury in sample of largemouth bass fillets from the 2005 sampling (0.30 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory is justified. This advisory was issued by IDNR and IDPH in January 2006. According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “not supported.” Follow up sampling conducted in 2007 and 2009 also showed that the levels of mercury in largemouth bass (0.412 ppm and 0.534 ppm, respectively) were above the one meal per week consumption advisory. Therefore the consumption advisory remains at this lake and the fish consumption uses are assessed as "not supported."
